Use wide char version of Windows API (#8390)

This PR modernizes the Windows-specific code by replacing ANSI Windows
API functions with their Unicode (wide character) counterparts. This
change ensures proper handling of Unicode file paths and strings on
Windows systems.

### File Operations (`source/core/slang-io.cpp`)
- `DeleteFileA` → `DeleteFileW`
- `GetTempPathA` → `GetTempPathW` 
- `GetTempFileNameA` → `GetTempFileNameW`
- `RemoveDirectoryA` → `RemoveDirectoryW`
- `SHFileOperationA` → `SHFileOperationW`
- `GetModuleFileNameA` → `GetModuleFileNameW` with UTF-8 conversion

### Platform Operations (`source/core/slang-platform.cpp`)
- `GetModuleHandleExA` → `GetModuleHandleExW`
- `LoadLibraryExA` → `LoadLibraryExW`
- `LoadLibraryA` → `LoadLibraryW`
- `OutputDebugStringA` → `OutputDebugStringW`

### Runtime and Tools
- `MessageBoxA` → `MessageBoxW` in slang-rt
- `GetCurrentDirectoryA` → `GetCurrentDirectoryW` in slang-fiddle
- String literal conversion to wide strings in vk-pipeline-create

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Gangzheng Tong <gtong-nv@users.noreply.github.com>
Co-authored-by: slangbot <ellieh+slangbot@nvidia.com>
Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

5 files changed, 64 insertions, 37 deletions

diff --git a/source/core/slang-io.cpp b/source/core/slang-io.cpp
index 0720e788f..36c8c560d 100644
--- a/source/core/slang-io.cpp
+++ b/source/core/slang-io.cpp
@@ -48,8 +48,9 @@ namespace Slang
 /* static */ SlangResult File::remove(const String& fileName)
 {
 #ifdef _WIN32
-    // https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-deletefilea
-    if (DeleteFileA(fileName.getBuffer()))
+
+    // https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-deletefilew
+    if (DeleteFileW(fileName.toWString()))
     {
         return SLANG_OK;
     }
@@ -77,10 +78,10 @@ namespace Slang
         int count = MAX_PATH + 1;
         while (true)
         {
-            char* chars = tempPath.prepareForAppend(count);
+            wchar_t* wideChars = (wchar_t*)_alloca(count * sizeof(wchar_t));
             //  Gets the temp path env string (no guarantee it's a valid path).
-            // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettemppatha
-            DWORD ret = ::GetTempPathA(count - 1, chars);
+            // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettemppathw
+            DWORD ret = ::GetTempPathW(count - 1, wideChars);
             if (ret == 0)
             {
                 return SLANG_FAIL;
@@ -90,7 +91,7 @@ namespace Slang
                 count = ret + 1;
                 continue;
             }
-            tempPath.appendInPlace(chars, count);
+            tempPath = String::fromWString(wideChars);
             break;
         }
     }
@@ -104,19 +105,18 @@ namespace Slang
     String tempFileName;
 
     {
-        int count = MAX_PATH + 1;
-        char* chars = tempFileName.prepareForAppend(count);
+        wchar_t wideChars[MAX_PATH + 1];
 
-        // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettempfilenamea
+        // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettempfilenamew
         // Generates a temporary file name.
         // Will create a file with this name.
-        DWORD ret = ::GetTempFileNameA(tempPath.getBuffer(), prefix.getBuffer(), 0, chars);
+        DWORD ret = ::GetTempFileNameW(tempPath.toWString(), prefix.toWString(), 0, wideChars);
 
         if (ret == 0)
         {
             return SLANG_FAIL;
         }
-        tempFileName.appendInPlace(chars, ::strlen(chars));
+        tempFileName = String::fromWString(wideChars);
     }
 
     SLANG_ASSERT(File::exists(tempFileName));
@@ -768,8 +768,8 @@ SlangResult Path::remove(const String& path)
     {
     case SLANG_PATH_TYPE_FILE:
         {
-            // https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-deletefilea
-            if (DeleteFileA(path.getBuffer()))
+            // https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-deletefilew
+            if (DeleteFileW(path.toWString()))
             {
                 return SLANG_OK;
             }
@@ -777,8 +777,8 @@ SlangResult Path::remove(const String& path)
         }
     case SLANG_PATH_TYPE_DIRECTORY:
         {
-            // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-removedirectorya
-            if (RemoveDirectoryA(path.getBuffer()))
+            // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-removedirectoryw
+            if (RemoveDirectoryW(path.toWString()))
             {
                 return SLANG_OK;
             }
@@ -810,20 +810,26 @@ SlangResult Path::remove(const String& path)
     // Path::remove() doesn't support remove a non-empty directory, so we need to implement
     // a simple function to remove the directory recursively.
 #ifdef _WIN32
-    // https://learn.microsoft.com/en-us/windows/win32/api/shellapi/nf-shellapi-shfileoperationa
+    // https://learn.microsoft.com/en-us/windows/win32/api/shellapi/nf-shellapi-shfileoperationw
     // Note: the fromPath requires a double-null-terminated string.
-    String newPath = path;
-    newPath.append('\0');
-    SHFILEOPSTRUCTA file_op = {
+    // Convert to wide string first, then manually create double-null-terminated buffer
+    auto widePath = path.toWString();
+    Index widePathLen = wcslen(widePath);
+    wchar_t* doubleNullPath = (wchar_t*)_alloca((widePathLen + 2) * sizeof(wchar_t));
+    wcscpy(doubleNullPath, widePath);
+    doubleNullPath[widePathLen] = L'\0';     // First null terminator
+    doubleNullPath[widePathLen + 1] = L'\0'; // Second null terminator for SHFileOperationW
+
+    SHFILEOPSTRUCTW file_op = {
         NULL,
         FO_DELETE,
-        newPath.begin(),
+        doubleNullPath,
         nullptr,
         FOF_NOCONFIRMATION | FOF_NOERRORUI | FOF_SILENT,
         false,
         0,
         nullptr};
-    int ret = SHFileOperationA(&file_op);
+    int ret = SHFileOperationW(&file_op);
     if (ret)
     {
         return SLANG_FAIL;
@@ -973,13 +979,28 @@ static SlangResult _calcExectuablePath(char* outPath, size_t* ioSize)
     SLANG_ASSERT(bufferSize > 0);
 
 #if SLANG_WINDOWS_FAMILY
-    // https://docs.microsoft.com/en-us/windows/desktop/api/libloaderapi/nf-libloaderapi-getmodulefilenamea
+    // https://docs.microsoft.com/en-us/windows/desktop/api/libloaderapi/nf-libloaderapi-getmodulefilenamew
 
-    DWORD res = ::GetModuleFileNameA(::GetModuleHandle(nullptr), outPath, DWORD(bufferSize));
+    // Use wide character version and convert back to UTF-8
+    wchar_t* widePath = (wchar_t*)_alloca(bufferSize * sizeof(wchar_t));
+    DWORD res = ::GetModuleFileNameW(::GetModuleHandle(nullptr), widePath, DWORD(bufferSize));
     // If it fits it's the size not including terminator. So must be less than bufferSize
     if (res < bufferSize)
     {
-        return SLANG_OK;
+        // Convert back to UTF-8
+        int utf8Len = WideCharToMultiByte(
+            CP_UTF8,
+            0,
+            widePath,
+            -1,
+            outPath,
+            (int)bufferSize,
+            nullptr,
+            nullptr);
+        if (utf8Len > 0)
+        {
+            return SLANG_OK;
+        }
     }
     return SLANG_E_BUFFER_TOO_SMALL;
 #elif SLANG_LINUX_FAMILY
diff --git a/source/core/slang-platform.cpp b/source/core/slang-platform.cpp
index 25e6bc6f0..75c1b96cd 100644
--- a/source/core/slang-platform.cpp
+++ b/source/core/slang-platform.cpp
@@ -122,7 +122,7 @@ SLANG_COMPILE_TIME_ASSERT(E_OUTOFMEMORY == SLANG_E_OUT_OF_MEMORY);
     handleOut = nullptr;
     if (!platformFileName || strlen(platformFileName) == 0)
     {
-        if (!GetModuleHandleExA(0, nullptr, (HMODULE*)&handleOut))
+        if (!GetModuleHandleExW(0, nullptr, (HMODULE*)&handleOut))
             return SLANG_FAIL;
         return SLANG_OK;
     }
@@ -131,12 +131,14 @@ SLANG_COMPILE_TIME_ASSERT(E_OUTOFMEMORY == SLANG_E_OUT_OF_MEMORY);
     // First attempt tries on the directories explicitly specified with AddDllDirectory(),
     // If it failed to find one, we will search over all PATH.
     // Windows API made two approaches mutually exclusive and we need to try two times.
-    // https://learn.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-loadlibraryexa
-    HMODULE h = LoadLibraryExA(platformFileName, nullptr, LOAD_LIBRARY_SEARCH_USER_DIRS);
-    // If LoadLibraryExA failed, try again with LoadLibraryA.
-    // https://docs.microsoft.com/en-us/windows/desktop/api/libloaderapi/nf-libloaderapi-loadlibrarya
+    // https://learn.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-loadlibraryexw
+    String platformFileNameStr(platformFileName);
+    HMODULE h =
+        LoadLibraryExW(platformFileNameStr.toWString(), nullptr, LOAD_LIBRARY_SEARCH_USER_DIRS);
+    // If LoadLibraryExW failed, try again with LoadLibraryW.
+    // https://docs.microsoft.com/en-us/windows/desktop/api/libloaderapi/nf-libloaderapi-loadlibraryw
     if (!h)
-        h = LoadLibraryA(platformFileName);
+        h = LoadLibraryW(platformFileNameStr.toWString());
     // If still not found, return an error.
     if (!h)
     {
@@ -356,7 +358,8 @@ static const PlatformFlags s_familyFlags[int(PlatformFamily::CountOf)] = {
 /* static */ SlangResult PlatformUtil::outputDebugMessage([[maybe_unused]] const char* text)
 {
 #ifdef _WIN32
-    OutputDebugStringA(text);
+    String textStr(text);
+    OutputDebugStringW(textStr.toWString());
     return SLANG_OK;
 #else
     return SLANG_E_NOT_AVAILABLE;
diff --git a/source/slang-rt/slang-rt.cpp b/source/slang-rt/slang-rt.cpp
index 35ffdb138..d264ae300 100644
--- a/source/slang-rt/slang-rt.cpp
+++ b/source/slang-rt/slang-rt.cpp
@@ -16,7 +16,7 @@ extern "C"
     {
         fprintf(stderr, "%s", errorMessage.getBuffer());
 #if SLANG_WINDOWS_FAMILY
-        MessageBoxA(0, errorMessage.getBuffer(), "Slang Runtime Error", MB_ICONERROR);
+        MessageBoxW(0, errorMessage.toWString(), L"Slang Runtime Error", MB_ICONERROR);
 #endif
         abort();
     }
diff --git a/tools/slang-fiddle/slang-fiddle-main.cpp b/tools/slang-fiddle/slang-fiddle-main.cpp
index cf8407995..fea16dafe 100644
--- a/tools/slang-fiddle/slang-fiddle-main.cpp
+++ b/tools/slang-fiddle/slang-fiddle-main.cpp
@@ -425,9 +425,12 @@ int main(int argc, char const* const* argv)
     }
     fprintf(stderr, "\n");
 
-    char buffer[1024];
-    GetCurrentDirectoryA(sizeof(buffer), buffer);
-    fprintf(stderr, "cwd: %s\n", buffer);
+    wchar_t wideBuffer[1024];
+    GetCurrentDirectoryW(sizeof(wideBuffer) / sizeof(wideBuffer[0]), wideBuffer);
+
+    // Convert to UTF-8 using String::fromWString
+    String currentDir = String::fromWString(wideBuffer);
+    fprintf(stderr, "cwd: %s\n", currentDir.getBuffer());
     return 1;
 #endif
 
diff --git a/tools/vk-pipeline-create/main.cpp b/tools/vk-pipeline-create/main.cpp
index 91abb90bc..5685affb4 100644
--- a/tools/vk-pipeline-create/main.cpp
+++ b/tools/vk-pipeline-create/main.cpp
@@ -278,8 +278,8 @@ void PipelineCreationReplay::initVulkanAPI(IDevice* device)
     vkAPI.device = (VkDevice)(handle.handles[2].value);
     vkAPI.instance = (VkInstance)(handle.handles[0].value);
 #if SLANG_WINDOWS_FAMILY
-    auto dynamicLibraryName = "vulkan-1.dll";
-    HMODULE module = ::LoadLibraryA(dynamicLibraryName);
+    auto dynamicLibraryName = L"vulkan-1.dll";
+    HMODULE module = ::LoadLibraryW(dynamicLibraryName);
     vkAPI.vulkanLibraryHandle = (void*)module;
 #define VK_API_GET_GLOBAL_PROC(x) vkAPI.x = (PFN_##x)GetProcAddress(module, #x);
 #else